People are always looking for a unique way to commemorate some event, for example, birthday, bar mitzvah, graduation, wedding, anniversary, death, athletic victory, etc.; or send a greeting or gift to others at a holiday such as Valentines day or Christmas.
Even before the landing of Apollo XI in 1969, which returned images from that expedition of the first boot prints of humans on the surface of the Moon, human beings have dreamed about leaving their own mark on other worlds. While the actual rate of deterioration of these foot prints and wheel tracks left in the lunar soil will remain unknown until humans or their robotic explorers can return to study them, the general scientific consensus is that these marks will remain discernible for possibly many millennia. They may be longer lasting evidence of human civilization than the pyramids of ancient Egypt.
Advances in astronautics and aerospace engineering over the past 50 years have made it possible to offer equipment which will permit people to reach out and touch, figuratively speaking, surfaces of other bodies in our solar system. Twin, telerobotically operated, Soviet Lunokhod moon rovers of the early 1970s collectively traveled almost 47 km during a combined 15 months of operation; and also by the success of the American Mars Exploration Rovers, Spirit and Opportunity, which operated for over 5 years on the surface of Mars collectively traveling over 21 kilometers by the end of 2008 using a combined telerobotic and autonomous mode of operation.